I remember reading about some language in which both [t] and [k] were considered the same phoneme and one of the [t] and [k] were used in formal and the other in informal settings. Does such a language exist or was what I read a myth? I apologize for being vague but I have no other information about that language and it is bugging me.
There are a few Polynesian languages such as Hawaiian and Samoan that don't contrast [t] and [k] i.e. [t] and [k] exist as allophones of /t/.
The language you're looking for seems to be Samoan where /t/ is pronounced [k] in colloquial speech and [t] in formal speech.
K (Depending on the person) is used in everyday speech, though T is used to greet people formerly. So, T is replaced with K, similar to how Tongans replace the sound of their Ts with a D, but in Samoa you can choose to speak which ever style you like depending on the situation.
4Hi, Hamo, and welcome to the site! Which language are you referring to in this answer? Samoan?– Draconis ♦Mar 23 at 23:58